SYNOPTIC MAPS OF POLAR CAPS FOR STABLE INTERPLANETARY MAGNETIC-FIELD INTERVALS DURING JANUARY 1992 GEOSPACE ENVIRONMENT MODELING CAMPAIGN

Observations from January 27-28, 1992,when four polar-orbiting DMSP sa tellites were in operation, are used to construct synoptic maps of con vective flows and particle regions within the polar ionosphere. We cho se periods of relative steady interplanetary magnetic field (IMF) and use data from multiple satellite passes during each period to obtain u nprecedented two-dimensional coverage. For strongly negative IMF B-y, convection patterns are similar to those that have been previously obt ained but also show significant IMF B-z effects. For B-z much greater than \B-y\, we see strong sunward flow near the pole, but antisunward convection on open field lines at lower latitudes on the nightside. Th e particle observations reveal the two-dimensional structure of the cu sp/mantle region and the existence of a strong polar are within the ci rcular convection cell that has a negative electric field divergence o n open field lines. The particle observations also readily identify th e magnetic separatrix when a satellite crosses the inner edge of the c usp :or the boundary between the plasma sheet and polar rain. However, on the morningside and often on the afternoonside, we find a distinct and well-defined region of soft-electron and magnetosheath-like ion p recipitation [(the ''soft-electron zone'' (SEZ)] lying between the pla sma sheet and the region of polar rain. Separatrix-identification is u ncertain at local times where the SEZ is present; however, it appears that large portions of the SEZ are on open field lines. Dawn-dusk disp lacements of the open field line regions in the two polar caps are see n that are consistent with IMF B-y effects. Additionally, the dayside separatrix is observed to be further poleward for positive than for ne gative IMF B-z, whereas B-z is not observed to have a significant effe ct on the location of the nightside separatrix. Also, we consistently find larger cross polar-cap potential drops in the southern hemisphere than in the northern hemisphere. This suggests that there are signifi cant (tens of kV) magnetic-field-aligned potential drops along high-al titude regions of open field lines where the magnetic field is weak an d particle motion strongly violates the guiding center approximation.